1) Field of the Invention
This invention relates to a laser welding method and a laser welding apparatus, particularly to a laser welding method and a laser welding apparatus using a small laser welding head which can precisely weld bodies to be welded in a good quality without an entire gas shielding for the bodies.
2) Description of Related Art
Recently, with the advance of high-power laser welding technique, a high-power CO2 laser welding technique is used for a macro welding, and a YAG laser welding technique is used for a precise welding. The reason is that the above techniques have the following advantages, in comparison with other welding techniques such as a TIG welding technique and a MIG welding technique.
(1) Large welding ratio (welding depth/melting bead width), and small processing strain
(2) High speed welding, and being capable of providing a high quality welded joint through little remaining thermal efficiency and repressing the increase of crystalline grains
(3) Being capable of performing a welding process in a canister with a transparent window having a peculiar atmosphere therein
(4) Being capable of welding different kinds of metal or a metal and a non-metal
Moreover, the above techniques have the following advantages, in comparison with an electron beam welding technique.
(5) Not be influenced by the magnetic field of bodies to be welded, and thus, being capable of welding a magnetic material
(6) Not requiring a vacuum chamber and a X-ray shielding.
On the contrary, in the above-mentioned laser welding technique, the melting part of the bodies to be welded is chemically reacted to an atmosphere gas around the bodies, and particularly, if the melting part is oxidized by a nearby air, the weld bead is disadvantageously degraded. As a result, a coaxial nozzle is attached to the laser welding head, and thus, for preventing the oxidization of the melting part, a shielding gas such as Ar gas or He gas is blown on a part to be welded of the bodies to be welded, which corresponds to the melting part, at the same time when a converged laser is irradiated to the part to be welded.
However, even if the shielding gas is blown on the part to be welded, the melting part often chemically reacts, and thus, is often oxidized. As a result, an exogenous material is generated at and taken in the welded part of the bodies to be welded through the chemical reaction and the oxidization, resulting in the degradation of the welded part.
Consequently, for preventing the above chemical reaction and oxidization, it is obliged to perform the laser welding process in a steel case having a shielding gas to prevent the oxidization (chemical reaction) after the steel case is evacuated. On account of this process, a large-scale and complicate laser welding apparatus is needed.
Furthermore, the above shielding gas may be partially taken in the weld bead by a large amount, so that, if the welded body is employed under an ultra-high vacuum atmosphere of not more than 10xe2x88x925 Pa or a hyperultra-high vacuum atmosphere of not more than 10xe2x88x929 Pa, the partially taken-in shielding gas is gradually emitted, resulting in the degradation of the vacuum degree.
It is an object of the present invention to bring out the advantages and characteristics of the above laser welding by ironing out the above-mentioned matters, that is, to provide a laser welding method and a laser welding apparatus which can prevent the oxidization and the chemical reaction of the welded part of the bodies to be welded by shielding parts to be welded of the bodies perfectly from an outside air and maintaining the shielded atmosphere, and can reduce the shielding gas emission from the weld bead for the welded body be able to be employed in such an ultra-high vacuum atmosphere or a hyperultra-high vacuum atmosphere.
For achieving the above object, this invention is directed at a laser welding method for welding plural bodies to be welded comprising the steps of:
blowing an inert gas on a part to be welded from a coaxial nozzle,
blowing a compressed shielding gas around the part to be welded so as to cover the inert gas from at least one discharging nozzle provided at the outer side of the coaxial nozzle, and
irradiating a converged laser onto the part to be welded, and thus, melting the part under the shielded condition from an outside air to weld the plural bodies.
Moreover, this invention is directed at a laser welding apparatus for welding plural bodies to be welded comprising:
a coaxial nozzle to blow an inert gas on a part to be welded,
at least one discharging nozzle, provided at the outer side of the coaxial nozzle, to blow a compressed shielding gas around the part to be welded so as to cover the inert gas,
a laser oscillator to oscillate a laser, and
a condenser to converge the laser, and thus, melt the part to be welded through the irradiation of the converged laser under the shielded condition from an outside air to weld the plural bodies.
The other objects, configurations and advantages will be explained in detail, with reference to the attaching drawings.